JP2016102237A - Titanium plate, plate for heat exchanger, separator for fuel battery and method for producing titanium plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a titanium plate combining high strength and high moldability applicable to heat exchangers and fuel batteries.SOLUTION: Provided is a titanium plate having a composition containing, by mass, 0.020 to 1.000% Fe and 0.020 to 0.400% O, and the balance titanium with inevitable impurities and having a crystal grain structure of an α phase with an HCP structure, in which the circle equivalent diameter in the crystal grains of the α phase is 20 to 100 μm by the average value and 300 μm or lower by the maximum value, and when, in the directions parallel to the plate surface. The direction in which 0.2% proof stress is the minimum is defined as the minimum proof stress direction and the direction orthogonal to the minimum proof direction. The 0.2% proof stress in the minimum proof stress direction is defined as YSand the 0.2% proof stress in the orthogonal proof stress direction is defined as YS, the ratio YS/YSis 1.17 or lower, and plate thickness is 1.0 mm or lower.SELECTED DRAWING: None

Description

  The present invention relates to a titanium plate made of industrially pure titanium, a heat exchanger plate using the titanium plate, and a fuel cell separator.

  In general, titanium plates are excellent in specific strength and corrosion resistance, so they can be used for heat exchanger parts such as chemical, electric power and food manufacturing plants, consumer products such as camera bodies and kitchen equipment, and transportation of motorcycles and automobiles. It is used for exterior materials such as equipment members and home appliances. Titanium plates are used in plate-type heat exchangers, which are being applied in recent years, among them, because high heat exchange efficiency is required. ing. Therefore, a titanium plate for a heat exchanger is required to have excellent formability in order to have a deep wave. Furthermore, a titanium plate for a heat exchanger is required to have a certain strength or more in order to realize durability improvement and weight reduction required as a heat exchanger.

  Titanium plates that are frequently used for various applications are defined in the JIS H4600 standard, and there are grades such as JIS type 1, type 2 and type 3 depending on the impurity concentration and strength of Fe, O, etc. The strength is increased, and they are properly used according to the application. Conventionally, a JIS type 1 pure titanium plate (with a proof stress of 165 MPa or more) having a low concentration of Fe or O has been used as a member requiring high formability because of its low strength but high ductility. However, in recent years, in addition to improving the efficiency of heat exchangers, there has been an increasing demand for higher strength and lighter weight. As a titanium plate that meets this requirement, for example, a JIS type 2 pure titanium plate (with a proof stress of 215 MPa or more) can be cited. However, when the strength level of such a pure titanium plate is reached, it is difficult to apply to a heat exchanger. It is. In general, titanium materials can be strengthened by increasing the concentration of impurities such as Fe and O and by making crystal grains finer. However, these methods greatly reduce the formability.

Therefore, the following has been proposed for improving the formability of the titanium plate.
For example, in Patent Document 1, in a method for producing a pure titanium hot-rolled sheet, the final rolling direction of hot rolling is rolled so as to be perpendicular to the rolling direction of block rolling, and Manufacturing methods have been devised for obtaining titanium plates.

  In Patent Document 2, in the method for producing a Ti—Fe—O—N-based high-strength titanium alloy plate, in-plane anisotropy is not as complicated as cross-rolling, but is rolled only in a direction perpendicular to the rolling direction. A method for reducing the above has been devised.

  Patent Document 3 proposes a titanium plate having high yield strength and excellent press formability. In this titanium plate, the crystal grain size of α phase crystal grains is increased to increase the frequency of deformation twins during press molding. Furthermore, after the final annealing, skin pass rolling with a rolling reduction of 0.7 to 5.0% is performed to adjust the texture (shift angle of the C axis) to obtain a specified accumulated strain amount. By these, it is set as the titanium plate holding proof stress.

Japanese Patent Laid-Open No. 63-130753 Japanese Patent No. 3481428 Japanese Patent No. 5385038

However, the conventional techniques have the following problems.
The technique of Patent Document 1 is cross rolling in which rolling is also performed in a direction perpendicular to the rolling direction, and generally, cross rolling cannot be performed on a plate longer than the rolling roll width. For this reason, the technique of Patent Document 1 has a large limitation on the plate shape that can be rolled. Furthermore, since the hexagonal C-axis is oriented in the vicinity of the normal to the plate surface, the strength anisotropy is reduced, but it is inferior in local deformability and is not suitable for bending or stretch forming.

  The technique of Patent Document 2 is considered to have less restrictions than the technique of Patent Document 1, but in any case, it involves a large restriction on the plate shape that can be rolled. Furthermore, since the hexagonal C-axis is oriented in the vicinity of the normal to the plate surface, the strength anisotropy is reduced, but it is inferior in local deformability and is not suitable for bending or stretch forming.

  The technique of Patent Document 3 has room for improvement in productivity because the number of processes increases in order to perform skin pass rolling. Moreover, there is room for further improvement in the balance between strength and formability.

  The present invention has been made in view of the above problems, and has a titanium plate having high strength and high formability applicable to a heat exchanger and a fuel cell, a plate for a heat exchanger using the same, and a fuel It is an object of the present invention to provide a battery separator.

The inventors have reduced the difference in strength between the rolling direction and the rolling width direction (that is, strength anisotropy) and controlled the crystal grain size within an appropriate range to balance strength and formability. It was found that can be improved.
Specifically, it is as follows.

The titanium plate according to the present invention contains Fe: 0.020 to 1.000 mass%, O: 0.020 to 0.400 mass%, and the balance is made of titanium and inevitable impurities, and has an HCP structure. A titanium plate including a phase grain structure, wherein an equivalent circle diameter in the α phase grain is 20 to 100 μm on an average value and 300 μm or less on a maximum value, and 0 in a direction parallel to the plate surface. the direction minimum .2% yield strength and minimum strength direction, when the direction perpendicular to the minimum yield strength direction perpendicular strength direction, the 0.2% proof stress of the minimum yield strength direction and YS _R, of the orthogonal strength directions 0.2% yield strength _YS T / YS _R is the ratio when the YS _T is 1.17 or less, wherein the thickness is 1.0mm or less.

  According to the above configuration, the titanium plate of the present invention contains a predetermined amount of Fe and O, so that the strength is increased and the moldability is improved. In addition, the titanium plate defines the equivalent circle diameter in the α-phase crystal grains and also defines the ratio of 0.2% proof stress between the minimum proof stress direction and the orthogonal proof stress direction, thereby improving formability. In addition, by defining the plate thickness, the titanium plate is suitable for forming a groove shape when producing a heat exchanger plate or a fuel cell separator.

In the titanium plate of the present invention, the standard deviation of the equivalent circle diameter in the α-phase crystal grains is preferably 10 to 40.
According to the said structure, intensity | strength anisotropy reduces more by prescribing | regulating the standard deviation of the circle equivalent diameter in the crystal grain of (alpha) phase.

Moreover, it is preferable that the titanium plate of this invention further contains any 1 or more types of N: 0.050 mass% or less, C: 0.100 mass% or less, and Al: 1.000 mass% or less.
According to the said structure, it becomes possible to improve the intensity | strength of a titanium plate more. Furthermore, heat resistance can be improved by adding Al.

  The heat exchanger plate of the present invention is a heat exchanger plate using the titanium plate described above, and has a pitch of 4t to 40t and a depth of 5t to 15t when the plate thickness is t (mm). It has one groove or two or more grooves.

  The fuel cell separator of the present invention is a fuel cell separator using the above-described titanium plate, and has a pitch of 4t to 40t and a depth of 5t to 15t when the plate thickness is t (mm). It is characterized by having one groove or two or more grooves.

  The plate for a heat exchanger and the separator for a fuel cell of the present invention are excellent in heat transfer efficiency or reduced in weight.

According to the titanium plate according to the present invention, it is possible to provide high formability capable of being pressed into a heat exchanger plate or a fuel cell separator while having high strength.
The plate for a heat exchanger and the separator for a fuel cell according to the present invention are excellent in heat transfer efficiency or lightening effect.

It is a perspective view for demonstrating the minimum proof stress direction and an orthogonal proof stress direction in the titanium plate of this invention. It is a process flow figure showing a manufacturing method of a titanium plate. In an Example, it is a typical top view which shows the shape of the shaping die for performing a moldability evaluation. It is EE sectional drawing of FIG.

Hereinafter, embodiments of the present invention will be described in detail.
[Titanium plate]

The titanium plate according to the present invention contains a predetermined amount of Fe and O, and the balance is made of titanium and inevitable impurities, and includes an α-phase crystal grain structure having an HCP structure (that is, a hexagonal close-packed structure). It is a board.
The titanium plate defines an equivalent circle diameter in the α-phase crystal grains. Further, as shown in FIG. 1, the titanium plate has a minimum proof stress direction 2 in the direction parallel to the plate surface (that is, the surface of the titanium plate 1) and has the minimum 0.2% proof stress. when the direction orthogonal to the direction 2 perpendicular strength direction 3, the ratio of the time the 0.2% proof stress of the minimum yield strength direction 2 and YS _R, the 0.2% yield strength of the orthogonal strength directions 3 was YS _T YS _T / YS _R is defined. In general, the minimum proof stress direction 2 often coincides with the rolling direction. Furthermore, the titanium plate defines the plate thickness.
Each configuration will be described below.

(Fe: 0.020 to 1.000 mass%)
The strength of the titanium plate decreases when the Fe content is low. Further, in order to produce a titanium plate having an Fe content of less than 0.020% by mass, high-purity sponge titanium is applied as a raw material, which increases costs. Therefore, the Fe content is 0.020% by mass or more.
On the other hand, when a large amount of Fe is contained, segregation of the ingot increases and productivity decreases. Therefore, the Fe content is 1.000% by mass or less. The Fe content is preferably 0.250% by mass or less, more preferably 0.120% by mass or less, from the viewpoint of further improving productivity.

(O: 0.020-0.400 mass%)
The strength of the titanium plate decreases when the O content is low. Further, in order to produce a titanium plate having an O content of less than 0.020% by mass, high-purity sponge titanium is applied as a raw material, which increases the cost. Therefore, the O content is 0.020% by mass or more. The O content is preferably 0.030% by mass or more from the viewpoint of further improving the strength and productivity.
On the other hand, when a large amount of O is contained, the titanium plate becomes brittle and cracks during cold rolling tend to occur, resulting in a decrease in productivity and a decrease in formability. Therefore, O content shall be 0.400 mass% or less. From the viewpoint of further improving productivity and moldability, the O content is preferably 0.200% by mass or less, more preferably 0.130% by mass or less, and further preferably 0.100% by mass or less.

  The titanium plate according to the present invention may contain H, N, C, Al, Si, Cr, Ni, and the like as unavoidable impurities in addition to Fe, O, and Ti (titanium). In particular, N, C, and Al may be added in excess of the content as an inevitable impurity, and the titanium plate according to the present invention has N: 0.050 mass% or less, C: 0.100 mass% or less. , Al: It is preferable to further contain any one or more of 1.000% by mass or less.

(N: 0.050 mass% or less, C: 0.100 mass% or less, Al: 1.000 mass% or less)
When N, C, and Al are added in excess of their content as inevitable impurities, the strength of the titanium plate is improved, and further, Al improves the heat resistance. In order to obtain these effects, the content of N, C, and Al is preferably 0.001% by mass or more.
On the other hand, if the titanium plate contains excessive N, C, and Al, cracks during cold rolling are likely to occur, and productivity is reduced. In particular, C makes the titanium plate brittle. When C is contained, the C content is 0.100% by mass or less. C content is 0.050 mass% or less preferably from a viewpoint of suppressing the said malfunction more. Moreover, when it contains N, N content shall be 0.050 mass% or less. When it contains N, it is 0.014 mass% or less from a viewpoint of suppressing the said malfunction more. Moreover, when it contains Al, Al content shall be 1.000 mass% or less. The Al content is preferably 0.400% by mass or less, more preferably 0.200% by mass or less, from the viewpoint of further suppressing the above problems.

(Remainder: titanium and inevitable impurities)
The components of the titanium plate are as described above, and the balance consists of titanium and inevitable impurities. Inevitable impurities are contained within a range that does not impair the various characteristics of the titanium plate, and are H, N, C, Al, Si, Cr, Ni, and the like. The contents of N, C, and Al are as described above. For other elements, H: 0.005% by mass or less, and other elements: each 0.1% by mass or less, the present invention. It does not inhibit the effect and is allowed.

As shown in FIG. 1, the titanium plate according to the present invention has a minimum 0.2% yield strength in a direction parallel to the surface of the titanium plate 1 and a direction perpendicular to the minimum yield strength direction 2 and the minimum yield strength direction 2. Is the 0.2% proof stress (YS _R ) in the minimum proof stress direction 2 and the 0.2% proof stress (YS _T ) in the orthogonal proof stress direction 3 (YS _T / YS _R ) 1.17 or less. This figure is obtained empirically from many experiments.
If the ratio of 0.2% proof stress exceeds 1.17, excellent moldability cannot be obtained. Therefore, the ratio of 0.2% proof stress is defined as 1.17 or less. The ratio of 0.2% proof stress is preferably 1.15 or less, more preferably 1.10 or less, from the viewpoint of further improving moldability. The ratio of 0.2% proof stress is 1.0 because of the principle, and the best characteristic is exhibited.
In plate forming, the deformation is accompanied by a reduction in the cross section in the plate thickness direction, resulting in fracture. However, as the plate thickness is relatively reduced, the amount of deformation in the plate thickness direction is reduced. Therefore, control of the yield strength ratio to achieve high formability is particularly important. The titanium plate of the present invention is assumed to be molded after that, but if the plate thickness is thick, the bending deformability is inferior and it cannot be molded with a fine pattern. Therefore, the upper limit of the plate thickness is set to 1.0 mm or less. In general, as the plate thickness decreases, the cold rolling reduction ratio increases. Therefore, in the related art, it is difficult to reduce the strength anisotropy as the plate thickness decreases.
The ratio of 0.2% proof stress can be controlled by the final cold rolling rate and the final annealing holding temperature in the production of the titanium plate, as will be described later.

(Equivalent circle diameter of α phase crystal grains: average value 20 to 100 μm, maximum value 300 μm or less)
In the titanium plate according to the present invention, if the α phase crystal grain size is too coarse, the formability is deteriorated even if the strength anisotropy is reduced. In particular, as the plate thickness decreases, the number of crystal grains in the plate thickness direction decreases, and the deterioration tendency becomes remarkable.
Therefore, the equivalent circle diameter of the α-phase crystal grains (that is, the diameter of the circle having the same area as the cross section of the crystal grains) is 100 μm or less on average and 300 μm or less on maximum. The circle equivalent diameter of the α-phase crystal grains is preferably 60 μm or less on average from the viewpoint of further improving the moldability. Further, the equivalent circle diameter of the α-phase crystal grains is preferably 250 μm or less at the maximum value, more preferably 200 μm or less at the maximum value from the viewpoint of further improving the moldability.
In addition, since it is difficult to make the equivalent circle diameter of the α phase crystal grains less than 20 μm while reducing the strength anisotropy, the equivalent circle diameter of the α phase crystal grains is 20 μm or more on average. The average value is preferably 25 μm or more.

Moreover, it is preferable that the standard deviation of the equivalent circle diameter of the α phase crystal grains is 10 to 40.
(Standard deviation of circle equivalent diameter of α phase crystal grains: 10 to 40)
Although the mechanism by which the standard deviation affects the strength formability is not necessarily clear, the strength anisotropy can be further reduced when α-phase crystal grains having different sizes are mixed.
The effect can be obtained if the standard deviation of the equivalent circle diameter is 10 or more. Therefore, the standard deviation of the equivalent circle diameter is preferably 10 or more. From the viewpoint of further improving the effect, it is more preferably 15 or more, and further preferably 20 or more. On the other hand, if the standard deviation of the equivalent circle diameter is 40 or less, coarse α-phase crystal grains are hardly formed, and formability is improved. The standard deviation of the equivalent circle diameter is more preferably 35 or less from the viewpoint of further improving the moldability.

  The crystal grain size of the α phase can be controlled by the holding temperature and holding time of the final annealing in the production of the titanium plate, as will be described later. Further, the crystal grain size of the α phase is an arbitrary cross section of the titanium plate and is a plate material, and therefore can be measured by observing a plane parallel to the rolled surface of the titanium plate. Specifically, the surface (plate surface) of the titanium plate is polished to form an observation surface, and an electron backscatter diffraction (EBSD) method is performed while scanning this surface with an electron beam with a scanning electron microscope (SEM). Then, the EBSD pattern is measured and analyzed, a boundary having an orientation difference of 10 ° or more is recognized as a crystal grain boundary, and a region surrounded by the crystal grain boundary is defined as a crystal grain.

(Thickness: 1.0mm or less)
Since the titanium plate according to the present invention is suitable for forming a groove shape such as a heat exchanger plate or a fuel cell separator, the plate thickness is 1.0 mm or less. When the thickness of the titanium plate exceeds 1.0 mm, when a fine groove shape is provided by molding, wrinkles are likely to occur, and a desired precise groove shape cannot be obtained. Moreover, the deformation resistance at the time of molding becomes high, which is not preferable, and the cost increases. Therefore, the thickness of the titanium plate is 1.0 mm or less. The plate thickness is preferably 0.7 mm or less from the viewpoint of moldability and cost. On the other hand, the thickness of the titanium plate is preferably 0.05 mm or more in order to easily obtain practical strength as a heat exchanger plate and a fuel cell separator. The plate thickness is more preferably 0.07 mm or more from the viewpoint of further improving the strength.

The titanium plate of the present invention can be used to form a heat exchanger plate and a fuel cell separator that are excellent in heat transfer efficiency or lightening effect.
Specifically, when the thickness of the titanium plate is set to t (mm), by providing one or more grooves having a pitch of 4t to 40t and a depth of 5t to 15t, it is more than conventional. It can be formed into a complex shape (pitch and depth correspond to, for example, the pitch and maximum depth of the molding die of FIG. 4). That is, it becomes possible to deepen the groove, narrow the groove width to narrow the pitch, or form an arbitrary pattern. As a result, the surface area of the formed titanium plate can be increased, the flow of the heat medium (liquid, gas) is homogenized, and a heat exchanger plate and a fuel cell separator exhibiting excellent heat transfer efficiency are obtained. Can do. Furthermore, even with the same heat transfer efficiency, the thickness can be reduced as the strength increases, and a lightweight heat exchanger plate and a fuel cell separator can be obtained.

[Production method of titanium plate]
The titanium plate is manufactured by the following manufacturing method, for example.
As shown in FIG. 2, the titanium plate manufacturing method includes a titanium material manufacturing step S1, a hot rolling step S2, an annealing step S3, a cold rolling step S4, an intermediate annealing step S5, It includes an inter-rolling step S6 and a final annealing step S7, which are performed in this order. Note that the annealing step S3 and the intermediate annealing step S5 may not be performed. Alternatively, only one of annealing step S3 and intermediate annealing step S5 may be performed. Here, the case where annealing before cold rolling is performed and intermediate annealing is performed once is illustrated. Further, as will be described later, after the cold rolling step S6, the intermediate annealing step and the cold rolling step may be performed a plurality of times.
Hereinafter, each step will be described.

(Titanium material manufacturing process S1)
The titanium material manufacturing step S1 manufactures a titanium material containing Fe and O and the balance of titanium and inevitable impurities, or a titanium material further containing N, C and Al before the hot rolling step S2. It is a process to do. When manufacturing a titanium plate, first, in the same way as when manufacturing a conventional titanium plate, an ingot is manufactured (that is, an ingot (which is pure titanium for industrial use)), and this ingot is split forged or rolled. Thus, a titanium material for use in the subsequent steps is obtained. The method of ingot production, partial forging, or partial rolling is not particularly limited, and may be performed by a conventionally known method. For example, first, a raw material of a predetermined component is melted by a consumable electrode type vacuum arc melting method (VAR method) or an electron beam melting method (EB method), and then cast to obtain a titanium ingot. This ingot is split-forged into a block shape of a predetermined size (hot forging) to obtain a titanium material. The components such as Fe are as described above.

(Hot rolling process S2)
The hot rolling step S2 is a step of performing hot rolling on the titanium material. The method of hot rolling is not particularly limited, and may be performed by a conventionally known method. For example, hot rolling may be performed by heating to 700 to 1050 ° C.

(Annealing step S3)
The annealing step S3 is a step of annealing the hot rolled sheet produced in the above step. The annealing method is not particularly limited, and may be performed by a conventionally known method. For example, it is preferable to anneal the hot-rolled sheet at a holding temperature (ie, annealing temperature) of 600 to 850 ° C.

(Cold rolling step S4, intermediate annealing step S5, cold rolling step S6)
Cold rolling process S4, S5 is a process which cold-rolls to the hot-rolled sheet in which annealing was given. The method of cold rolling is not particularly limited, and may be performed by a conventionally known method.
The total rolling reduction by cold rolling (that is, the processing rate with respect to the hot rolled sheet) is preferably 20 to 98%. In addition, you may perform the annealing (namely, intermediate annealing) similar to the said cold rolling in the middle of cold rolling. Further, intermediate annealing and cold rolling may be performed a plurality of times. That is, the intermediate annealing step S5 may be performed after the cold rolling step S4, and then the cold rolling step S6 (final cold rolling step) may be performed. Further, when the intermediate annealing is performed a plurality of times, after the intermediate annealing step S5 and the cold rolling step S6, the intermediate annealing and the cold rolling are further performed once or more in this order.

Among the intermediate annealing and cold rolling consisting of a plurality of times, the cold rolling after the final intermediate annealing (that is, the final cold rolling) has a reduction rate (that is, the final cold rolling rate) of 20 to 87%. . That is, it is necessary to set the rolling reduction ratio of the cold rolling process immediately before the final annealing process S7 to 20 to 87%. If the rolling reduction exceeds 87%, a desired low strength anisotropy cannot be obtained even if final annealing described later is performed. The final cold rolling rate is preferably 70% or less from the viewpoint of easily obtaining low strength anisotropy. In addition, when not performing intermediate annealing, the cold rolling performed after hot rolling or after annealing in annealing process S3 is made into final cold rolling (cold rolling process S4 turns into a final cold rolling process).
The intermediate annealing is preferably performed at a holding temperature of 600 to 850 ° C. (that is, annealing temperature), similarly to the annealing temperature in the annealing step.

  Annealing and intermediate annealing before cold rolling may be performed in any atmosphere of air, vacuum, inert gas such as Ar, and reducing gas, and can be performed in either a batch furnace or a continuous furnace. In particular, when annealing is performed in an air atmosphere (ie, air annealing), the scale is attached to the surface of the titanium plate (ie, hot-rolled plate), so the next step (following cold rolling if intermediate annealing) is performed. It is preferable to perform, for example, a salt heat treatment, a pickling treatment, etc. as the scale removal step.

(Final annealing process)
The final annealing step S7 is a step of performing final annealing after the final cold rolling.
The titanium plate according to the present invention controls the crystal grain size and strength anisotropy of the α phase by adjusting the temperature and time in the final annealing. Specifically, the annealing temperature is set to a β transformation point (T _β ) or more and less than 950 ° C. The β transformation point is the lowest temperature at which the entire titanium plate (that is, cold-rolled plate) (that is, 100%) becomes the β phase, and varies depending on the composition of titanium (that is, Fe content, etc.).

  In the annealing prior to cold rolling and the intermediate annealing, as described above, the annealing temperature is, for example, a general annealing condition of a pure titanium material, that is, 600 ° C. or higher where recrystallization proceeds and less than the β transformation point. It is 850 degrees C or less. Under such conditions, by not increasing the fraction of β phase, the growth of α phase crystal grains is not hindered and grows in equiaxed grains. In contrast, in the final annealing, the entire cold-rolled sheet is transformed into the β phase by heating to the β transformation point or higher, that is, the β single phase region. By subsequently cooling, the strength anisotropy can be reduced by transforming from the β phase to the α phase. The cooling rate is preferably 10 ° C./second or more. However, the higher the temperature in the β single phase region, the more the growth of β phase crystal grains is promoted, and the larger the annealing temperature becomes 950 ° C., the larger the crystal grains of the α phase formed thereafter. To do.

Further, as the holding time at the annealing temperature becomes longer, the β-phase crystal grains become larger. When the final annealing holding time exceeds 180 seconds, the β phase crystal grains become coarse. Therefore, the annealing temperature (holding temperature) in the final annealing step is set to the β transformation point or higher and lower than 950 ° C., and the holding time in this temperature range is set to 180 seconds or shorter. The holding time includes 0 seconds. The holding time of 0 seconds means that the cold-rolled plate is heated and cooled as soon as it reaches the β transformation point.
The final annealing may be any atmosphere of air, vacuum, inert gas, or reducing gas. In addition, when it anneals to air | atmosphere, it is preferable to perform a scale removal process as above-mentioned after cooling.

  The titanium plate according to the present invention can have the α phase crystal grain structure defined above by performing cold rolling and final annealing under predetermined conditions.

  The manufacturing method of the titanium plate is as described above. However, when manufacturing the titanium plate, other steps may be included before or after each step within a range not adversely affecting each step. Good. For example, when the scale adheres to the titanium plate surface after each annealing, a step of removing the scale may be included. Examples of the process for removing the scale include a salt heat treatment process and a pickling process. In addition, for example, a foreign matter removing step for removing foreign matter on the surface of the titanium plate, a defective product removing step for removing defective products generated in each step, and the like may be included.

  The titanium plate of the present invention is a heat exchanger member such as a chemical, electric power or food production plant, a consumer product such as a camera body or a kitchen device, a transport device member such as a motorcycle or an automobile, or an exterior material such as a home appliance. It can be used as a separator for fuel cells. In particular, it can be suitably used for a plate-type heat exchanger that requires excellent formability.

  As mentioned above, although the form for implementing this invention has been described, the Example which confirmed the effect of this invention is demonstrated concretely compared with the comparative example which does not satisfy | fill the requirements of this invention below. It should be noted that the present invention is not limited by this embodiment, and can be implemented with modifications within the scope shown in the claims, all of which are included in the technical scope of the present invention.

[Test material preparation]
N or the like was added to a pure titanium (JIS H4600) ingot, and the pure titanium ingot was melted and cast by the VAR method to obtain a titanium ingot having the composition shown in Table 1. This titanium ingot was subjected to ingot forging (that is, hot forging) and hot rolling to obtain a hot rolled sheet having a thickness of 4.0 mm. The scale on the surface of the hot rolled sheet was removed, and cold rolling, intermediate annealing, and final cold rolling were performed to obtain a cold rolled sheet having a thickness of 0.50 mm. The cold-rolled sheet was subjected to final annealing under the conditions shown in Table 1, and desalted by a salt bath process and pickling to obtain a test material having a sheet thickness of 0.45 mm. The cooling rate after heating in the final annealing step was about 80 ° C./second (calculated by linear approximation up to 700 ° C.). Further, based on the composition of the test material, the β transformation point (T _β ) is calculated using thermodynamic calculation software “ThermoCalc” and is also shown in Table 1.

[Evaluation]
(Measurement of α phase crystal grains)
The surface of the test material (i.e., the plate surface) is polished, and 1.6 mm square (i.e., 1 each in the rolling direction and the rolling width direction) on the rolling surface having a plate thickness of 1/2 part (i.e., plate thickness center). .6 mm) region was observed by EBSD. The EBSD measurement was performed by the FE-SEM / EBSD method. The measurement data was analyzed using EBSD data analysis software, a boundary having an orientation difference of 10 ° or more was set as a crystal grain boundary, and the equivalent circle diameter of each crystal grain was calculated. Table 1 shows the average and maximum values of equivalent circle diameters.

(Tensile test, strength anisotropy evaluation)
A No. 13 test piece defined in JISZ2201 was cut out from the test material, and a tensile test was performed at room temperature based on JIS H4600. At this time, when the rolling direction (referred to as RD) is set as the load axis direction, it is confirmed that it becomes the minimum proof stress direction. Here, the minimum proof stress direction is the rolling direction and the orthogonal proof stress direction is the rolling width direction (TD). ) as performed at room temperature tensile test, 0.2% proof stress (respectively in the rolling direction and the rolling width _direction, YS R, and YS _T) was measured to calculate the _YS T / YS _R as strength anisotropy, Each is shown in Table 1. 1.17 or less is accepted.

(Evaluation of formability)
Evaluation of formability was performed by performing press molding using a molding die simulating a heat exchange portion (that is, a plate) of a plate heat exchanger for each test material.
As shown in FIGS. 3 and 4, the shape of the molding die is such that the molding part is 100 mm × 100 mm, there are four twill line parts with a pitch of 17 mm and a maximum depth of 6.5 mm, and each twill line part is at the apex. , R = 2.5 mm.
Using this molding die, press molding was performed by an 80-ton press. In press molding, rust preventive oil was applied to both surfaces of each test material for lubrication, and the test material was placed on the lower mold so that the rolling direction of each test material coincided with the vertical direction of FIG. And after constraining the flange portion with a plate press, the mold was pushed in under the condition of a press speed of 1 mm / sec. The mold was pushed in at intervals of 0.1 mm, and the maximum amount of indentation depth (E: unit mm) at which no cracks occurred was determined by experiment. Then, the formability index (F) was calculated by the following formula. The results are shown in Table 1. In addition, it was set as the pass when the moldability index (F) was a positive value.
F = E− (GH−YS)
G = 7.00, H = 0.0120
YS = Numerical value of 0.2% proof stress in the RD direction (rolling direction) E = Numerical value of the maximum indentation depth

  As shown in Table 1, test material No. In Nos. 1 to 13, the definition of the equivalent circle diameter of the α-phase crystal grains and the strength anisotropy were within the scope of the present invention, and excellent strength and formability were maintained in a well-balanced manner.

On the other hand, the test body No. which is a comparative example. 14-24 became the following results.
Specimen No. 14,15,17,18,19,20,23, the holding temperature in the final annealing is lower than T _beta, strength anisotropy poor moldability without reduction.
Specimen No. Nos. 16 and 21 had a long retention time in the final annealing, so that the maximum value of the circle equivalent diameter of the α grains exceeded the upper limit. As a result, although the strength anisotropy was lowered, the moldability was poor.

Specimen No. In No. 22, since the holding temperature in the final annealing was high, the maximum value of the equivalent circle diameter of α grains exceeded the upper limit. As a result, although the strength anisotropy was lowered, the moldability was poor.
Specimen No. In No. 24, since the cold rolling ratio of the final cold rolling was high, the strength anisotropy was not sufficiently lowered, and the formability was poor.

  The present invention has been described in detail with reference to the embodiments and examples. However, the gist of the present invention is not limited to the above-described contents, and the scope of right is widely interpreted based on the description of the claims. Must. Needless to say, the contents of the present invention can be widely modified and changed based on the above description.

1 Titanium plate 2 Minimum proof stress direction 3 Orthogonal proof stress direction

The present invention relates to a titanium plate made of industrially pure titanium, a heat exchanger plate and a fuel cell separator using the titanium plate, and a method for producing the titanium plate .

The present invention has been made in view of the above problems, and has a titanium plate having high strength and high formability applicable to a heat exchanger and a fuel cell, a plate for a heat exchanger using the same, and a fuel It is an object of the present invention to provide a battery separator and a method for producing the titanium plate .

Claims (5)

Titanium containing Fe: 0.020 to 1.000 mass%, O: 0.020 to 0.400 mass%, the balance being composed of titanium and inevitable impurities, and having an α-phase crystal grain structure of HCP structure A board,
The equivalent circle diameter in the α-phase crystal grains is 20 to 100 μm in average value and 300 μm or less in maximum value,
Of the directions parallel to the plate surface, the direction with the minimum 0.2% proof stress is the minimum proof stress direction, and the direction perpendicular to the minimum proof stress direction is the orthogonal proof stress direction, the 0.2% proof stress of the minimum proof stress direction. was a YS _R, 0.2% yield strength of the orthogonal strength directions, which is the ratio of when the _{YS T} YS _T / YS _R is not less 1.17 or less,
A titanium plate having a plate thickness of 1.0 mm or less.   2. The titanium plate according to claim 1, wherein a standard deviation of a circle-equivalent diameter in the α-phase crystal grains is 10 to 40. 3.   The titanium plate further contains any one or more of N: 0.050 mass% or less, C: 0.100 mass% or less, and Al: 1.000 mass% or less. Or the titanium plate of Claim 2.   It is a plate for heat exchangers using the titanium plate of any one of Claims 1-3, Comprising: When it is set as plate | board thickness t (mm), pitch is 4t-40t and depth is 5t- A plate for a heat exchanger having one or more grooves of 15t.   A fuel cell separator using the titanium plate according to any one of claims 1 to 3, wherein when the plate thickness is t (mm), the pitch is 4t to 40t and the depth is 5t to 5t. A fuel cell separator having one or two or more grooves of 15t.

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